I. Field
The present invention relates generally to electronics, and more specifically to techniques for mitigating the deleterious effects of a transmit (TX) leakage signal in a wireless full-duplex communication system.
II. Background
A wireless device in a wireless full-duplex communication system can simultaneously transmit and receive data for two-way communication. One such full-duplex system is a Code Division Multiple Access (CDMA) system. On the transmit path, a transmitter within the wireless device (1) modulates data onto a radio frequency (RF) carrier signal to generate an RF modulated signal and (2) amplifies the RF modulated signal to obtain a transmit signal having the proper signal level. The transmit signal is routed via a duplexer and transmitted from an antenna to one or more base stations. On the receive path, a receiver within the wireless device (1) obtains a received signal via the antenna and duplexer and (2) amplifies, filters, and frequency downconverts the received signal to obtain baseband signals, which are further processed to recover data transmitted by the base station(s).
For a full-duplex wireless device, the RF circuitry in the receiver is often subjected to interference from the transmitter. For example, a portion of the transmit signal typically leaks from the duplexer to the receiver, and the leaked signal (which is commonly referred to as a “TX leakage” signal or a “TX feed-through” signal) may cause interference to a desired signal within the received signal. Since the transmit signal and the desired signal typically reside in two different frequency bands, the TX leakage signal can normally be filtered out and does not pose a problem in itself. However, the TX leakage signal may interact with a “jammer” (which is a large amplitude undesired signal close in frequency to the desired signal) to generate “cross modulation” distortion components on both sides of the jammer, as described below. Distortion components that fall within the signal band of the desired signal and which are not filtered out act as additional noise that may degrade performance.
A surface acoustic wave (SAW) filter is often used to filter out the TX leakage signal and mitigate its deleterious effects. The use of a SAW filter for TX leakage rejection is undesirable for several reasons. First, the SAW filter is normally a discrete component that is not fabricated on an RF integrated circuit (RFIC) and thus occupies space on a circuit board. Second, the SAW filter typically requires other discrete components for input and output impedance matching. Third, the SAW filter and its impedance matching circuitry increase the cost of the wireless device.
There is therefore a need in the art for techniques to mitigate the deleterious effects of a TX leakage signal without using a SAW filter.